| 摘要 |
PROBLEM TO BE SOLVED: To generate a signal (phase signal) based on phase information on the basis of emitted light including two different pieces of phase information, and to accurately detect positional information of a moving mobile with an output device on the basis of the phase signal. SOLUTION: An encoder operates photoelectric conversion signals I<SB>a</SB>, I<SB>b</SB>, I<SB>c</SB>and I<SB>d</SB>from a light receiving element 26, and calculates two signals I<SB>A</SB>and I<SB>B</SB>as the result. A signal I<SB>AB</SB>is generated from the signals I<SB>A</SB>and I<SB>B</SB>, and is output from the encoder 10. The term of the signal I<SB>AB</SB>depending on time (t) is 4dsin(ωt) as shown in expression (7): I<SB>AB</SB>=I<SB>A</SB>×I<SB>B</SB>=4sinϕcosϕ=2sin(2ϕ)=2sin[8πx/p-4dsin(ωt)]. The term of the signal I<SB>A</SB>and I<SB>B</SB>depending on time (t) is 2dsin(ωt) as shown in expression (5): I<SB>A</SB>=I<SB>a</SB>-I<SB>c</SB>=2cos[4πx/p-2dsin(ωt)] and expression (6): I<SB>B</SB>=I<SB>b</SB>-I<SB>d</SB>=2sin[4πx/p-2dsin(ωt)]. The signal I<SB>AB</SB>varies with respect to the signals I<SB>A</SB>and I<SB>B</SB>similarly to the manner that degree of modulation d is substantially doubled. Accordingly, when the position of a moving scale 24 is detected based on the signal I<SB>AB</SB>, the position of the moving scale 24 can be detected in the degree similar to that when the degree of modulation d is doubled. COPYRIGHT: (C)2008,JPO&INPIT
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